Optical transmitters are devices that send optical signals over optical signal transmission media in optical and optoelectronic networks. Typically, an optical transmitter is included with optical receiver in an optical transceiver. Recently, multi-channel optical transceivers have been made to communicate multiple signals over a single medium.
Multiple wavelength division multiplexing (WDM) has been used for optical interfaces for data rates at 40 Gbps (e.g., 40 GBASE LR4 and ER4) and 100 Gbps (e.g., 100 GBASE LR4 and ER4). The IEEE 802.3ba-2010 standard defines four WDM channels multiplexed onto a single fiber for these interfaces. The 40 GBASE-LR4/ER4 interface defines CWDM grids with center wavelengths of 1271, 1291, 1311, and 1331 nm. The 100GBASE-LR4/ER4 interface defines LAN-WDM channels with center wavelengths of 1295.56, 1300.05, 1304.58, and 1309.14 nm.
FIG. 1 shows a transmitter/receiver path in a conventional 40GBASE-LR4/ER4 or 100GBASE-LR4/ER4 communication system 10. The 40GBASE-LR4/ER4 or 100GBASE-LR4/ER4 communication system 10 includes a four-channel communication path. Generally, optical transceivers are at both ends of the path in the system 10, but for purposes of explaining signal transmission along the path, optical transmitters 32-38 are shown at one end of the path and optical receivers 72-78 are shown at the other end of the path. In the optical communication system 10, four separate electrical signals L0 through L3 are received by a retimer (e.g., buffer) 20, where the signals are synchronized and sent to respective optical transmitters 32-38 as parallel signals TP1<0:3> through a first PMD service interface 25. The optical transmitters 32-38 convert the electrical signals TP1<0:3> to optical signals on four channels that are combined by wavelength division multiplexer 40 and transmitted over a patch cord 45 through a MDI 42.
The combined optical signals are transmitted over optical fiber/cable, through a second MDI 52, where the optical signals are demultiplexed (i.e., separated) by wavelength division demultiplexer 60 into the separate optical signals for processing by the optical receivers 72-78. The optical receivers 72-78 convert the separate optical signals on each channel into separate electrical signals TP4<0:3> through a second PMD service interface 75. At the same time, AND gate 80 detects the presence of a signal on any of the channels at optical receivers 72-78 to inform external devices (e.g., in the network) that a signal has been received. The electrical signals TP4<0.3> are received by retimer 90, synchronized, and transmitted to various receiving devices elsewhere in the network.
For various reasons, it is important, if not critical, to fabricate compact, low cost optical subassemblies (OSAs) for use in such transceivers. Thus, there is demand for ever-smaller optical devices, particularly in multi-channel optical transmitters and transceivers.
This “Discussion of the Background” section is provided for background information only. The statements in this “Discussion of the Background” are not an admission that the subject matter disclosed in this “Discussion of the Background” section constitutes prior art to the present disclosure, and no part of this “Discussion of the Background” section may be used as an admission that any part of this application, including this “Discussion of the Background” section, constitutes prior art to the present disclosure.